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>> NGT and one of his humor sidekicks talking about the effects of
>> Special Relativity, and how General Relativity puts no constraints on
>> the rate of cosmic expansion.
>
> Google must save the correct link for me because I keep getting the same
> post by clicking on the link above.
>
>>
>>>>> The claim is that the expansion of space accelerated faster than light
>>>>> for parts of the universe that are no longer visible to us. Space
>>>>> expanded and nothing really accelerated to faster than light, but they
>>>>> are just too far away to observe. There was the initial inflation
>>>>> when
>>>>> space expanded much faster than the speed of light creating a "flat
>>>>> universe" with just the right amount of mass and energy to keep it
>>>>> from
>>>>> collapsing. Dark energy is supposed to account for the continued
>>>>> expansion of space within the universe. One article that I recall
>>>>> claimed that the visible universe extends out to around 45 billion
>>>>> light
>>>>> years in all directions from where we are. The visible light has
>>>>> to be
>>>>> younger than the age of our universe (less than 14 billion years), but
>>>>> space has expanded.
>>>>
>>>>
>>>> An important point is, according to the evidence, there was a time
>>>> before about 4bya when the universe was dominated by gravity, and its
>>>> rate of expansion was actually slowing. Now the universe is dominated
>>>> by dark energy, and so its rate of expansion has become ever faster
>>>> since then.
>>>
>>> The claim in the article is that the expansion of the universe continues
>>> to be currently accelerating, but the rate of acceleration is
>>> decreasing, so dark energy effects seem to have limits.
>>
>>
>> What you say above is contrary to what I have read:
>>
>> ********************************
>> In 1998, the High-Z Supernova Search Team published observations of
>> Type Ia ("one-A") supernovae. In 1999, the Supernova Cosmology Project
>> followed by suggesting that the expansion of the universe is
>> accelerating. The 2011 Nobel Prize in Physics was awarded to Saul
>> Perlmutter, Brian P. Schmidt, and Adam G. Riess for their leadership
>> in the discovery.
>> ********************************
>
> The original article noted that the expansion of the universe is still
> accelerating due to dark energy, but that the new measurements indicate
> that the rate of acceleration is decreasing over time. The expansion of
> space is still accelerating, but there seems to be less pressure on the
> gas petal so that the rate of accerleration is decreasing. The
> expansion is still going faster and faster, but the increased expansion
> rate is decreasing. If the decrease in acceleration continues there
> will come a time when the expansion rate is no longer increasing.
Not necessarily. The decrease in acceleration may approach zero
asymptotically. Keep dividing n by two, for example, and n will get
arbitrarily close to zero without ever reaching it.
Likewise, even if the *acceleration* actually drops to zero, that
doesn't mean the rate of increased expansion will drop to zero, or even
decrease. When a rocket stops accelerating, it maintains its current
speed until something stops it.
> The
> claim is that there is enough mass to start the collapse of the
> Universe. My guess is that the expansion will continue, but start to
> slow down instead of get faster and faster. Once the expansion stops,
> the universe can start to collapse.
>
>>
>>
>>> I recall an article claiming that our current visible universe extended
>>> out to around 45 billion light years in any direction (maybe it was 45
>>> billion light years across, the light within visible space has to be
>>> less than 14 billion years old) but there has to be a lot of the
>>> universe that we can no longer see. Kestrel indicated that this limit
>>> applied to the points within our visible universe so that every location
>>> had a different horizon and could see a different part of the existing
>>> universe. There would have to be a lot of matter that is not in the
>>> visible universe.
>>
>>
>> Correct. This is something I pointed out to Peter Nyikos awhile ago,
>> and I pointed out to you in my last post. Every point in the cosmos
>> is surrounded by its own Hubble Sphere. The working assumption is
>> that the cosmos outside our Hubble Sphere is largely similar to the
>> space inside. The problem is there is no way to know this for
>> certain, even in principle.
>
> So my original question was how do we know the amount of mass in the
> universe when there may be a near infinite amount that we cannot observe?
>
> The numbers on the internet that I have seen are that before the Big
> Bang all the mass in the universe was contained within a volume of a
> soccer ball. Another claim is that inflation took something like the
> size of a bacterium (1 to 10 microns) to the size of the Milky way
> galaxy that is 100,000 light years across. A soccer ball is 220,000
> microns in diameter. So my estimate would be that after inflation the
> universe would have already been over 2 billion light years across. The
> claim that I have seen was that there may have been enough mass to
> collapse the universe, but dark energy started an accelerated expansion
> of the universe where the rate of expansion kept increasing, and
> resulted in some of the universe to expand at a rate so fast that those
> parts of the universe would no longer be visible to us.
>
> We must have some type of mass estimate for the mass of the Big Bang,
> but is the mass that we cannot observe in our calculations estimating
> the mass of the universe based on what we can observe. The total mass
> of the universe has to be much greater than the visible mass we have
> been using to make our estimates of whether or not there is enough mass
> to cause a collapse. I have never read any account that would take into
> account that our visible universe is only a fraction of the volume of
> the total universe. Even the fact that there was a lot of the universe
> that was beyond the visible horizon was new to me due to the Webb
> telescope claims.
"How do we know the amount of mass in the universe" is another good
question. The short answer is: We look at the observable portions of the
universe and extrapolate, on the principle that our observable bubble
isn't notably different from the average conditions.
This isn't guaranteed to be true, of course: It's possible the space
beyond our cosmic event horizon is wall-to-wall black holes. Or it could
be utterly empty, and we're actually at the center of the universe. Or
the quantum vacuum state is higher or lower than it is here. Heck, maybe
the laws of physics as we know them are a localized phenomenon, and out
where we can't see them, things work in unimaginably different ways.
But science always requires some assumptions, somewhere.
>>>>> It doesn't matter, what I wanted was if the mass of the universe
>>>>> estimate includes the mass that is not observable. We have the
>>>>> background radiation map of the universe, and estimates based on
>>>>> what we
>>>>> can see (these are based on the observable universe). The estimates
>>>>> would have included what we could not see within the visible universe
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--- SoupGate-DOS v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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